Problem: $-\dfrac{4}{6} - \dfrac{1}{8} = {?}$
$ = - {\dfrac{4 \times 4}{6 \times 4}} - {\dfrac{1 \times 3}{8 \times 3}} $ $ = - {\dfrac{16}{24}} - {\dfrac{3}{24}} $ $ = - \dfrac{{16} - {3}}{24} $ $ = -\dfrac{19}{24}$